The present invention relates to a process for the formation of a glass body from a vitrifiable composition, and particularly to the coloring or modification of the color of such a body by diffusion of a substance into the surface layers of the body from a contacting medium.
It is known to fabricate bodies of colored, or tinted, glass by forming them from a vitrifiable composition into which appropriate coloring, or tinting, agents have been incorporated. However, such a process can be performed in only a limited number of cases, due to the necessity of utilizing a different starting composition for each color to be produced. In the glass industry, particularly in the fabrication of flat glass, it is normally much more practical to color, or tint, the glass bodies during or after their formation so that the coloring treatment can be controlled independently of the composition of the vitrifiable mixture and of the process for producing the glass.
Various methods for coloring a body of glass during or after its fabrication are known. Such methods include covering the glass body with a film of metal or metal oxide, by vapor deposition.
It is possible to produce, by such a method, a very thin film which only slightly reduces the light transmission of the body. However, such a film is subject to deterioration or removal by abrasion or by some mechanical or chemical action.
A more satisfactory known process consists in causing coloring substances to diffuse into the glass at an elevated temperature. By this procedure, it is possible to tint the glass to a certain depth from its surface and the resulting tinting cannot be removed by simple scratching of the glass surface. However, such diffusion processes offer only limited application possibilities if it is desired to color a series of different glasses.
When the known processes are performed, it often proves difficult to achieve a predetermined color density. The color density is a function of factors which cannot be varied entirely at will according to the desired color density, given that their value is critical for other reasons. This is particularly the case when the coloring treatment is carried out in apparatus in which the tempering of the glass is also effectuated.
The coloring elements which prove particularly valuable for various purposes are the elements of Group IB of Mendeleef's Periodic Table. The coloring achieved by means of these elements presents particular problems, given that the ions which diffuse into the glass must undergo a chemical reduction in order to impart a coloration to the glass.
It is advantageous to be able to perform a process in which silver, gold and copper can be utilized to color a body of ordinary soda lime glass and which can be easily controlled, in order to obtain different color densities. Silver, in particular, proves to be a desirable possible coloring agent. This agent is capable of giving glass a yellow color, or tint, which provides protection against actinic radiation.